Electronic circuit arrangement for controlling an exhaust gas decontaminator

ABSTRACT

A control circuit arrangement for an exhaust gas decontaminator is provided. A voltage generating circuit produces a voltage indicative of the recurrence frequency of the ignition pulses up to a desired limit engine speed, and a differentiating stage provides from the voltage generator signal a voltage to a threshold switch indicative of the engine acceleration. The threshold voltage output signal controls operation of the exhaust gas decontaminator.

[ 51 Sept. 11, 1973 ted tates atent Graewert [54] ELECTRONHC CIRCUIT ARRANGEMENT 3,548,791 12/1970 Long 123/32 EA FOR CONTROLLING AN EXHAUST GAS 3,673,989 7/1972 Aono et 123/127 X 3,685,295 8/1972 Tatsutomi et 123/1 17 A DECONTAMINATOR 2,953,898 9/1960 Cornelius.......................... 60/286 X Woitgang Kave Graewert,

[75] Inventor:

Wendlingen, Germany Primary ExaminerCarlton R. Croyle [73] Assignee: Texas Instruments lncoporated,

Dallas, Tex.

Assistant EJrarr irzer-Robert E, Garrett App]. No.: 205,182

[30] Foreign Apphcauon pnonty Data A control circuit arrangement for an exhaust gas de- Dec. 5, 1970 Germany................... P 20 59 951.3

contaminator is provided. A voltage generating circuit produces a voltage indicative of the recurrence fre quency of the ignition pulses up to a desired limit engine speed, and a differentiating stage provides from the voltage generator signal a voltage to a threshold switch indicative of the engine acceleration. The threshold voltage output signal controls operation of the exhaust gas decontaminator.

{56] References Cited UNITED STATES PATENTS 3,680,318 8/1972 Nakajima et al............ 123/117 A X 6 Claims, 2 Drawing Figures PATENTEI] SEP] 1 I975 SHEEI 1 0F 2 PATENTED SEPI I I575 sum 2 [IF 2 ELECTRONIC CIRCUIT ARRANGEMENT FOR CONTROLLING AN EXHAUST GAS DECONTAMINATOR BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to an electronic circuit arrangement for controlling an exhaust gas decontaminator which is to be actuated beneath a predetermined limit speed of the internal combustion engine when a predetermined acceleration is exceeded.

2. Description of the Prior Art Such exhaust gas decontaminators must be controlled in such a manner that beneath the limit speed (for example 3200 rpm) a device is set in operation which effects an additional decontamination of the exhaust gases when the acceleration exceeds a predetermined value (for example 55 rpm/s). On the other hand, the device must not be actuated whatever the acceleration above the limit speed.

It is therefore necessary to measure both the speed and the acceleration of the internal combustion engine and convert these measurements into control signals for the exhaust gas decontaminator. The mech anical devices hitherto used for this purpose are complicated and unreliable.

SUMMARY OF THE INVENTION The object of the invention is to provide an electronic circuit arrangement which with a simple and reliable construction makes it possible to control an exhaust gas decontaminator under the above conditions.

To solve this problem the circuit arrangement according to the invention contains a voltage generating circuit which is controlled by the ignition pulses of the internal combustion engine and which generates a voltage proportional to the recurrence frequency of the ig nition pulses, a maximum value limiting circuit connected to the output of the voltage generating circuit, a differentiating stage following the maximum value limiting circuit and a threshold value switching stage which is connected to the output of the differentiating stage and the output signal of which controls the exhaust gas decontaminator.

In the circuit arrangement according to the invention the speed is measured by measuring the recurrence frequency of the ignition pulses as in already known electrical tachometers. By differentiating a voltage propor-- tional to this recurrence frequency in the differentiating stage a voltage is obtained which is proportional to the acceleration. The following threshold value switching stage responds as soon as the voltage proportional to the acceleration exceeds a threshold value fixed to correspond to the predetermined acceleration at which the exhaust gas decontaminator must be actuated. The maximum value limiting circuit preceding the differentiating stage prevents the voltage proportional to the recurrence frequency of the ignition pulses and thus to the speed from exceeding a value which is chosen to correspond to the limit speed. Thus, above this limit speed the voltage applied to the differentiating stage no longer changes and consequently irrespective of the acceleration the differentiating stage cannot supply a signal which would cause the device to respond to the threshold value switching stage.

The invention thus solves the problem set in a simple and reliable manner. The circuit may be made very compact and cheaply, particularly by using the integrated circuit technique, and easily incorporated into any existing vehicle. By adjusting the limit threshold of the maximum value limiting circuit the limit speed can easily be varied, as can the response acceleration by adjusting the threshold valve of the threshold value switching stage, and consequently the circuit may easily be adapted to different engines and different operating conditions.

In a preferred embodiment of the invention the voltage generating circuit contains a pulse generator which is controlled by the ignition pulses and which produces pulses of constant width and amplitude whose frequency is propoi tional to that of the ignition pulses and a discriminator is connected to the output of the voltage generating circuit.

With this embodiment voltage generating circuits already commercially available may be used, such as those hitherto employed for electrical tachometers, an electrical indicating instrument then simply being connected to the voltage generating circuit, the deflection of said instrument being proportional to the mean DC value of the pulses produced and thus to the speed. In contrast, in the subject of the invention a discriminator is connected to the output of said voltage generating circuit and produces the voltage which is proportional to the recurrence frequency of the ignition pulses and which is thereafter further processed in the manner explained above.

BRIEF DESCRIPTION OF THE DRAWINGS:

FIG. 1 shows the block circuit diagram of a circuit arrangement according to the invention and FIG. 2 shows the more exact circuit diagram of a circuit of integrated construction based on the principle of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT:

A detailed description of a preferred embodiment of this invention follows with reference being made to the drawings wherein like parts have been given like reference numerals for clarity and understanding of the elements and features of the invention.

FIG. 1 of the drawings shows an input terminal 1 connected for example to the distributor of the internal combustion engine t receive the ignition pulses of the engine. Connected to'this input terminal is a pulse generating circuit 2 designed to produce pulses of constant width and constant amplitude whose recurrence frequency is equal or proportional to the recurrence frequency of the ignition pulses fed to the input. The recurrence frequency of these pulses is thus a measure of the speed of the engine. The pulse generating circuit 2 is followed by discriminator 3 which produces at its output a continuous voltage proportional to the mean DC value of the pulses supplied thereto and thus also proportional to the engine speed.

The output of the discriminator is followed by a maximum value limiting circuit 4 which allows the output voltage of the discriminator to pass unrestricted as long as said voltage is below a predetermined maximum value but which prevents said maximum value from being exceeded. The output of the maximum value limiting circuit 4 is fed to a differentiating stage 5 which produces an output voltage which is the derivative with respect to time of the input voltage thereof and is thus proportional to the acceleration of the internal combustion engine. This voltage is amplified in an. amplifier 6 and then applied to the input of a Schmitt trigger 7 which responds as soon as its input voltage reaches a predetermined threshold value. The output voltage of the Schmitt trigger 7 controls a switching stage 3 containing a relay 9 in its output. The relay 9 is thus energized as soon as the voltage applied to the input of the Schmitt trigger 7 reaches a predetermined value and drops out again when the Schmitt trigger 7 returns to the rest condition.

FIG. 2 shows a practical example of embodiment of the circuit of FIG. 1 which lends itself particularly well to monolithic integration. For this purpose the differentiating stage and the amplifier 6 are equipped with operational amplifiers. Diodes and Zener diodes are represented by suitably connected transistor diode paths.

The pulse generating circuit 2 is again represented only as a block. An integrated circuit arrangement known as Tacho-IC is preferably used for this purpose; it is available commercially and has hitherto been used for electrical revolution counters. Connected to the output of this pulse generating circuit is a potentiometer 10 whose tap is connected to the base of a transistor 11 which has the function of a reversing stage. The transistors 12 and 13 included in the collector circuit of the transistor 11 are connected as diodes and serve for temperature compensation.

The signal tapped off at the collector of the transistor 11 is fed to the discriminator 3 which operates on the principle of a counting discriminator and is provided with a complementary Darlington stage which is formed from an NPN transistor 14 and a PNP transistor 15. The transistor 16 connected as diode serves together with the transistor for simulating an integrated PNP transistor.

A voltage proportional to the mean DC value of the pulses supplied is taken from the emitter resistance 17 of the transistor 14. A filter net-work consisting of two electrolytic capacitors l8, l9 and a series resistance 20 is used to smooth said voltage. Connected to the output of this filter network is a transistor 21 which is connected as Zener diode and represents the maximum value limiter 4. The Zener diode ensures that the voltage stops increasing when a predetermined speed is reached so that the following circuit then no longer has any function. The limiting threshold of the Zener diode 21 is fixed but the desired relationship between the break-off voltage and the limit speed may be set by means of the potentiometer 10 at the output of the pulse generating circuit 2. It would of course alternatively be possible to make the limiting threshold of the maximum value limiter 4 adjustable in some way and to set the limit speed in this manner.

Below this limit speed the voltage taken off at the output terminal 22 of this smoothing and limiting circuit is proportional to the speed. It is applied via a differentiating capacitor 23 to the operational amplifier 24, which is degeneratively connected via a feedback resistance 25. The resistance 26 in series with the differentiating capacitor 23 and an integrating capacitor 27 parallel to the feedback resistance serve to filter out the AC voltage component in the frequencydependent output voltage of the discriminator.

Thus, there is obtained at the output terminal 23 of the operational amplifier 24 a voltage which is proportional to the acceleration; this voltage is amplified in the following amplifier stage 6 which also comprises an operational amplifier 29 degeneratively connected via a resistance 30. The gain of this amplifier stage is determined by the ratio of the input resistance 31 to the feedback resistance 34).

A transistor 32 connected as Zener diode produces a centre point voltage for the two operational amplifiers 2d and 29.

The output signal of the amplifier 6 is fed via a transistor 33, which is connected as Zener diode and reduces the output voltage, to the Schmitt trigger 7 formed in the usual manner from two transistors 34, 35. The transistors 36, 37 form the switching amplifier stage 8. A transistor 38 protects the transistor 37 from negative induction peaks. included in the output circuit of the switching amplifier stage is the relay 9 which is energized when the Schmitt trigger 7 responds and drives the switching amplifier stage 8.

By means of a potentiometer 40 at the first operational amplifier 24 the quiescent voltage at the output of the second operational amplifier 29 may be adjusted so that the switching operation is initiated when a predetermined acceleration occurs.

The transistors 41, 42, 43 serve to produce a stabilized voltage for the current supply of the circuit.

All the components within the dot-dash box 39 are part of the monolithic integrated circuit.

As an example it may be assumed that the limit speed is 3200 rpm. This corresponds to an ignition spark recurrence frequency of 107 cls in the case of a four cylinder four stroke engine.

The pulse generating circuit 2 is triggered by the ignition pulses and produces rectangular pulses having an amplitude of 2.3 volts and a duration of about 3,u.s. The recurrence frequency is determined by the engine speed.

An acceleration of 55 rpm/s corresponds to a frequency increase of 1.8 c/s/s. If for the range of 0 to 107 a voltage range of 5.6 V is available at the discriminator, the corresponding steepness is 52 mV/c/s. This quantity, multiplied by the acceleration quantity 1.8 c/s/s gives a rise rate of 94 mV/s for an acceleration of 55 rpm/s. This quantity must be differentiated with respect to time. With a differentiating circuit in the form of the differentiating capacitor 23 of capacitance C and the degeneratively connected operational amplifier 24 of resistance R if the gain is sufficiently large the output voltage U obeys the relationship wherein U, is the input voltage.

The capacitor 23 should not be an electrolytic capacitor because the useful current through the latter is of the order of magnitude of the leakage current. In the case of a capacitor of IOptF the current ther'ethrough with negligible input resistance (due to the negative feedback) is The leakage current of ordinary electrolytic capacitor is substantially higher whereas in the case of tantalum electrolytic capacitors it is of the same order of magnitude. For this reason, in the example given a compromise was made between capacitance and overall size and a 6.8ptF plastic foil capacitor with a 63 volt rated voltage was chosen. Because of the finite input resistance the resistance R of the negative feedback resistance 25 cannot be made infinitely high. A value of 180 kOhms was chosen. The output voltage of the differentiating state is thus:

This voltage is still too small to trigger the Schmitt trigger circuit and it is therefore amplified again by a factor of in the amplifier stage 6. For this purpose a negative feedback resistance 30 of 10 kOhms and an input resistance 31 of 1 kOhm are used.

What is claimed is:

l. A threshold control electrical circuit arrangement adapted to control the operation of an exhaust gas decontaminator associated with an internal combustion engine wherein the exhaust gas decontaminator is to be actuated only when the internal combustion engine is being operated at a speed below a predetermined limit speed while having a rate of acceleration exceeding a predetermined magnitude, said electrical circuit arrangement comprising:

a voltage signal generating circuit having an input terminal adapted to be connected to an internal combustion engine in such a manner as to receive the ignition pulses thereof, said voltage signal generating circuit being responsive to the ignition pulses of the internal combustion engine for generating a voltage signal proportional to the recurring frequency of the ignition pulses and representative of the speed of the internal combustion engine,

a maximum value limiting circuit connected to the output of the voltage signal generating circuit and having a predetermined maximum voltage threshold value, said maximum value limiting circuit being constructed to pass the output voltage signal from said voltage signal generating circuit to its own output provided its predetermined maximum voltage threshold value is not exceeded thereby but preventing the passage of the output voltage signal from said voltage signal generating circuit when its predetermined maximum voltage threshold value is exceeded thereby,

differentiating circuit means connected to the output of said maximum value limiting circuit for producing an output voltage as the derivative with respect to time of the input voltage received thereby such that the output voltage produced by said differentiating circuit means is representative of the rate of acceleration of the internal combustion engine, and

switching means operably associated with said differentiating circuit means and responsive to the output voltage of said differentiating circuit means upon said latter output voltage reaching a predetermined minimum voltage threshold value for producing an output signal adapted to actuate the exhaust gas decontaminator. 2. A threshold control electrical circuit arrangement as set forth in claim 1, wherein said voltage signal generating circuit includes a pulse generator connected to said input terminal and responsive to the ignition pulses of the internal combustion engine for producing pulses of constant width and amplitude having a frequency proportional to the frequency of the ignition pulses, and

discriminating circuit means connected to the output of said pulse generator and responsive thereto for producing a continuous voltage signal proportional to the mean DC value of the pulses applied at its input from said pulse generator, said continuous voltage signal being the output voltage signal of said voltage signal generating circuit.

3. Athreshold control electrical circuit arrangement as set forth in claim 2, further including a potentiometer interposed between said pulse generator and said discriminating circuit means, said potentiometer being connected to the output of said pulse generator and having an adjustable tap connected to the input of said discriminating circuit means.

4. A threshold control electrical circuit arrangement as set forth in claim 1, wherein said maximum value limiting circuit comprises a Zener diode connected at its input to the output of said voltage signal generating circuit.

5. A threshold control electrical circuit arrangement as set forth in claim 1, wherein said switching means includes a Schmitt trigger circuit connected at its input to the output of said differentiating circuit means.

6. A threshold control electrical circuit arrangement as set forth in claim 1, wherein said differentiating circuit means includes a capacitor and an operational amplifier connected in series, said capacitor being connected to the output of said maximum value limiting circuit and said operational amplifier being connected to the input of said switching means, said operational amplifier being provided with a feedback line connected at its output and extending back to its input at a connecting terminal located between said capacitor and said operational amplifierfand a resistor included in said feedback line.

a is m a In 

1. A threshold control electrical circuit arrangement adapted to control the operation of an exhaust gas decontaminator associated with an internal combustion engine wherein the exhaust gas decontaminator is to be actuated only when the internal combustion engine is being operated at a speed below a predetermined limit speed while having a rate of acceleration exceeding a predetermined magnitude, said electrical circuit arrangement comprising: a voltage signal generating circuit having an input terminal adapted to be connected to an internal combustion engine in such a manner as to receive the ignition pulses thereof, said voltage signal generating circuit being responsive to the ignition pulses of the internal combustioN engine for generating a voltage signal proportional to the recurring frequency of the ignition pulses and representative of the speed of the internal combustion engine, a maximum value limiting circuit connected to the output of the voltage signal generating circuit and having a predetermined maximum voltage threshold value, said maximum value limiting circuit being constructed to pass the output voltage signal from said voltage signal generating circuit to its own output provided its predetermined maximum voltage threshold value is not exceeded thereby but preventing the passage of the output voltage signal from said voltage signal generating circuit when its predetermined maximum voltage threshold value is exceeded thereby, differentiating circuit means connected to the output of said maximum value limiting circuit for producing an output voltage as the derivative with respect to time of the input voltage received thereby such that the output voltage produced by said differentiating circuit means is representative of the rate of acceleration of the internal combustion engine, and switching means operably associated with said differentiating circuit means and responsive to the output voltage of said differentiating circuit means upon said latter output voltage reaching a predetermined minimum voltage threshold value for producing an output signal adapted to actuate the exhaust gas decontaminator.
 2. A threshold control electrical circuit arrangement as set forth in claim 1, wherein said voltage signal generating circuit includes a pulse generator connected to said input terminal and responsive to the ignition pulses of the internal combustion engine for producing pulses of constant width and amplitude having a frequency proportional to the frequency of the ignition pulses, and discriminating circuit means connected to the output of said pulse generator and responsive thereto for producing a continuous voltage signal proportional to the mean DC value of the pulses applied at its input from said pulse generator, said continuous voltage signal being the output voltage signal of said voltage signal generating circuit.
 3. A threshold control electrical circuit arrangement as set forth in claim 2, further including a potentiometer interposed between said pulse generator and said discriminating circuit means, said potentiometer being connected to the output of said pulse generator and having an adjustable tap connected to the input of said discriminating circuit means.
 4. A threshold control electrical circuit arrangement as set forth in claim 1, wherein said maximum value limiting circuit comprises a Zener diode connected at its input to the output of said voltage signal generating circuit.
 5. A threshold control electrical circuit arrangement as set forth in claim 1, wherein said switching means includes a Schmitt trigger circuit connected at its input to the output of said differentiating circuit means.
 6. A threshold control electrical circuit arrangement as set forth in claim 1, wherein said differentiating circuit means includes a capacitor and an operational amplifier connected in series, said capacitor being connected to the output of said maximum value limiting circuit and said operational amplifier being connected to the input of said switching means, said operational amplifier being provided with a feedback line connected at its output and extending back to its input at a connecting terminal located between said capacitor and said operational amplifier, and a resistor included in said feedback line. 